electrolyte; the sulfuric acid is mixed with fumed silica, which makes the resulting mass gel like and immobile. Unlike a flooded wet cell lead–acid battery, these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage (and subsequent corrosion problems) common to the wet cell battery, and boast greater resistance to shock and vibration. Chemically they are almost the same as wet (non sealed) batteries except that the antimony in the lead plates is replaced by calcium, and gas recombination can take place. Applications Many modern motorcycles and all-terrain vehicles (ATVs) on the market use AGM batteries to reduce likelihood of acid spilling during cornering, vibration, or after accidents, and for packaging reasons. The lighter, smaller battery can be installed at an odd angle if needed for the design of the motorcycle. Due to the higher manufacturing costs compared with flooded lead–acid batteries, AGM batteries are currently used on luxury vehicles. As vehicles become heavier and equipped with more electronic devices such as navigation and stability control, AGM batteries are being employed to lower vehicle weight and provide better electrical reliability compared with flooded lead–acid batteries. 5 series BMWs from March 2007 incorporate AGM batteries in conjunction with devices for recovering brake energy using regenerative braking and computer control to ensure the alternator charges the battery when the car is decelerating. Vehicles used in auto racing may use AGM batteries due to their vibration resistance. Deep-cycle AGMs are also commonly used in off-grid solar power and wind power installations as an energy storage bank and in large-scale amateur robotics, such as the FIRST and IGVC competitions. AGM batteries are routinely chosen for remote sensors such as ice monitoring stations in the Arctic. AGM batteries, due to their lack of free electrolyte, will not crack and leak in these cold environments. VRLA batteries are used extensively in power wheelchairs, as the extremely low gas and acid output makes them much safer for indoor use. VRLA batteries are also used in the uninterruptible power supply (UPS) as a backup when the electrical power goes off. VRLA batteries are also the standard power source in sailplanes, due to their ability to withstand a variety of flight attitudes and a relatively large ambient temperature range with no adverse effects. However, charging regimes must be adapted with varying temperature. VRLA batteries are used in the US Nuclear Submarine fleet, due